#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <arpa/inet.h>


#define BUF_SIZE 30
void error_handling( char *msg);
void read_childproc( int sig );

int main(int argc, char *argv[])
{
    int serv_sock;
    int clnt_sock;
    struct sockaddr_in serv_addr;
    struct sockaddr_in clnt_addr;

    pid_t pid;
    struct sigaction act;
    socklen_t adr_sz;
    int str_len;
    int state;
    char buf[BUF_SIZE];

    if (2 != argc) {
        printf("Usage : %s <port> \n", argv[0]);
        exit(1);
    }
    act.sa_handler=read_childproc;
    sigemptyset(&act.sa_mask);
    act.sa_flags=0;
    state=sigaction(SIGCHLD, &act, 0);
    serv_sock=socket(PF_INET, SOCK_STREAM, 0);
    memset( &serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port =htons(atoi(argv[1]));

    if ( bind(serv_sock, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) == -1) {
        error_handling("bind() error");
    }
    if ( listen(serv_sock, 5) == -1 ) {
        error_handling("listen() error");
    }

    while (1) 
    {
        adr_sz = sizeof(clnt_addr);
        clnt_sock = accept(serv_sock, (struct sockaddr *) &clnt_addr, &adr_sz);
        if ( -1 == clnt_sock) {
            continue;
        }
        else{
            puts("new client connected...");
        } 
        pid = fork();
        if (-1 == pid) {
            close(clnt_sock);
            continue;
        }
        if (0 == pid ) {
            close(serv_sock);
            while (0 !=(str_len = read(clnt_sock, buf, BUF_SIZE)))
                write(clnt_sock, buf, str_len);
            
            close(clnt_sock);
            puts("client disconnected...");
            return 0;
        }
        else  {
            close(clnt_sock);
        }
    }
    close(serv_sock);
    return 0;
}
void read_childproc(int sig)
{
    pid_t pid;
    int status;
    pid=waitpid(-1, &status, WNOHANG);
    printf("removed proc id: %d \n", pid);
}
void error_handling(char *msg)
{
    fputs( msg, stderr);
    fputc('\n', stderr);
    exit(1);
}